The present invention relates to a rocker arm for use with a valve operating mechanism for an engine, and more particularly to a roller rocker arm using a roller at a contact portion to a cam.
FIG. 1 shows a conventional roller rocker arm as disclosed in Japanese Utility Model Laid-open No. 57-85653. Referring to FIG. 1, a body 05 of the roller rocker arm has two walls portions between which a space is defined. There is provided in the space a cylindrical outer ring 01 rotatably supported to the body 05 by using a bolt 07, a nut 071, an inner ring 031, and needle rollers 02.
The inner ring 031 is substantially cylindrical, and is held between both the wall portions of the body 05 by tightening the nut 071 to the bolt 07 passing through both the wall portions and an axial hole 036 of the inner ring 031. The inner ring 031 has an outer peripheral surface including small-diameter shoulder surfaces 035 formed at both longitudinal ends thereof and adapted to be engaged with doughnut-shaped collar rings 04 and a large-diameter raceway surface 034 formed between both the shoulder surfaces 035 and adapted to contact the needle rollers 02.
The outer ring 01 is formed with a small-diameter inner peripheral raceway surface 012 at a portion opposed to the outer raceway surface 034 of the inner ring 031, that is, at the portion on which the needle rollers 02 are rolled, and is further formed at its both ends with large-diameter shoulder surfaces 011 contacting outer peripheral surfaces 042 of the collar rings 04. Further, an outer peripheral surface 014 of the outer ring 01 contacts a cam plate 06.
In the above-mentioned arrangement, as the inner ring 031 is fixed to the body 05 by means of the bolt 07 and the nut 071, a weight of the bolt and the nut causes an increase in a whole weight of the rocker arm.
Furthermore, as the bolt 07 and the nut 071 project outwardly of the body 05, it is necessary to arrange adjacent parts so as to avoid the interference of the bolt 07 and the nut 071 in the case that the body 05 is displaced in association with the operation of the cam plate 06. Accordingly, the device is disadvantageously enlarged in size.
Additionally, the collar rings 04 are axially positioned by the shoulder portions of the inner ring 031, that is, they are designed not to rotate in association with the rolling operation of the needle rollers 02. Accordingly, in the event that an axial thrust load is applied to the needle rollers 02, there easily occurs seizure between the needle rollers 02 and the collar rings 04.